A seat apparatus for a vehicle such as an automobile, or the like, which is capable of adjusting an angle between a seat cushion serving as a seating portion and a seatback serving as a backrest portion, is known. This type of seat apparatus is provided with a seat cushion frame, a lower bracket fixed to the seat cushion frame, and a seatback frame mounted to the lower bracket through a reclining mechanism so as to be pivotally supported by the lower bracket.
According to the conventional seat apparatus for a vehicle disclosed in JP2004-81390A, the seatback frame is pivotally supported relative to the lower bracket through the reclining mechanism and the lower bracket is fixed to the seat cushion frame by means of two bolts. Thereby, an angle of the seatback relative to the seat cushion and the lower bracket is adjustable. For example, when an occupant is leaned on the seatback in a condition where the lower bracket is fastened and fixed to the seat cushion frame by means of one bolt, the force for pushing the seatback frame reward (i.e., a direction perpendicular to an axis line direction of a rotational shaft of the seat back frame) is generated and problem of rotating the lower bracket by making the one bolt as a support point may occur. However, according to the seat apparatus for a vehicle disclosed in JP2004-81390A, the lower bracket is fastened and fixed to the seat cushion frame by means of the two bolts. Therefore, even when the force for rotating the lower bracket by making one of the two bolts as the support point is applied to the direction perpendicular to the axis line direction of the rotational shaft of the seatback frame, the force can be received by the other bolt.
With the configuration of the seat apparatus for a vehicle disclosed in JP2004-81390A, the lower bracket is fixed to the seat cushion frame by means of the two bolts for preventing a relative rotation thereof. However, if the force for reclining the seatback frame reward is increased, the force for rotating the lower bracket by making the one bolt as the support point may highly be increased. On this occasion, the one bolt may be applied with an excessive shearing force. Accordingly, if large load is applied to the one of the two bolts, the bolt may be damaged. Further, the lower bracket and the seat cushion frame, which are in contact with the bolt, may be deformed. In order to prevent the one bolt from being applied with the large load, the lower bracket can be fixed to the seat cushion frame by means of more than two bolts so that the load may be dispersed to plural bolts. However, as the number of the bolts is increased, the problem of increasing the number of processes for fastening the lower bracket to the seat cushion frame may occur. Further, the problem of increasing the weight of the seat apparatus for a vehicle may occur.
The present invention has been made in view of the above circumstances, and provides a seat apparatus for a vehicle which can firmly connect the lower bracket with the seat cushion frame with a simple structure.